The present invention relates to a mechanism for securing mounting blocks for printing plate clamping devices on forme cylinders preferably of offset rotary printing presses.
In offset rotary printing presses it is necessary to securely clamp the printing plate on the outside surface of the forme cylinder, and for this purpose a printing plate clamping device is normally provided. However, since such printing plate clamping devices are continuously subjected to paper dust, ink, washing solutions, and the like, it must from time to time be dismantled for cleaning or any repairs that might be necessary. Because the printing press cannot be used during such cleaning or repairing, a reduction of the down time required for this purpose to insure minimum loss of time is desirable.
In designing a printing plate clamping device, one of the objectives is to make maximum use, for printing purposes, of the peripheral area available on the forme cylinder and accordingly it is desirable to make as small as possible the print-free space on the cylinder, i.e., the space which cannot be used for printing purposes as a result of the geometrical shape or condition of the printing plate clamping mechanism. To accomplish this, the mechanism of the printing plate clamping device is partly mounted in a cavity in the forme cylinder. The cavity is provided with a slot which is as narrow as possible and which opens to the surface of the cylinder, through which the end portions of the printing plate to be clamped are introduced into the printing plate clamping device. As required by the different constructions of available printing plate clamping devices, the cavities in the forme cylinder which receive the clamping devices have more or less complex inside cross sections.
The prior art suggests various possible methods for providing the cavities in the forme cylinder. For example, one or more inserts of a relative shape may be mounted into a paraxial canal, that is, a canal which extends parallel to the axis of the cylinder, or a properly sized hole may be drilled through the length of the cylinder. However, exact drilling of such long holes is difficult. The inserts are secured within the forme cylinder body by means of bolts, screws, or similar fasteners, with the fasteners extending from either the inner or the outer surface of the forme cylinder body. When the screws are inserted from the outer surface, the screwheads that protrude from the fitting holes are removed, as by turning, with the peripheral surface of the cylinder thereafter being ground so that a uniform smooth surface will result. It goes without saying that the screws holding the inserts in the forme cylinder body can no longer be removed.
With such prior arrangements mounting the printing plate clamping devices is not possible until the inserts have been firmly secured to the forme cylinder body. Further, because of the need to provide a print-free space as small as possible on the surface of the cylinder, the printing plate clamping device cannot be introduced, in many cases, into the cavity from the surface of the forme cylinder. This means that the printing plate clamping device must be mounted into the forme cylinder before the cylinder is mounted into its supporting side frame in the printing press. This is particularly true because it is impossible to introduce the long shafts, required for opening and closing the printing plate clamping device from the forme cylinder front side, into the inserts due to the space between the side frames and the forme cylinder front side having only a few centimeters of width. For the same reason, it is impossible to remove the printing plate clamping device from the forme cylinder as long as the cylinder remains mounted in the side frames. However, such dismantling of the printing plate clamping device may become necessary, for example, in order to replace a defective part, or else for cleaning the device carefully for guaranteeing its continued operation.